JPS5852527A - Temperature sensor - Google Patents

Abstract

PURPOSE:To remarkably elevate a characteristic, and to obtain a titled sensor which is excellent in its sensitivity and response speed, by using a piezoelectric crystal substrate itself on which a surface acoustic wave element has beed formed, as a light leading window. CONSTITUTION:An example in which a temperature sensor 6 has been formed on both a thin plate 12 and a substrate 13 having a lens-like reverse side is shown in the figure. Infrared rays from an object whose temperature is measured are made incident from the reverse side of an LiNbO3 crystal substrate, a piezoelectric crystal such as LiNbO3, etc. is transparent against the infrared rays, the quantity of absorption is extremely small, and its sensitivity and response speed become quicker than that which has used silicon or infrared ray transmitting glass as a transmitting window.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature sensor that uses a surface acoustic wave element and has excellent sensitivity and response speed.

A surface acoustic wave element has a structure in which comb-shaped electrodes are provided on a piezoelectric crystal surface for converting an electric signal into a surface acoustic wave, and is a solid element having functions such as a filter, a delay line, and a resonator.

Figure 1 is a front view of a surface acoustic wave device with a force of 1'>.
An input transformer 2 and an output transformer 3 having intersecting comb-shaped electrodes are formed on a piezoelectric crystal substrate 1 made of LiTaO, etc. When an electric signal is applied to the electrode 4 of the input transformer 2, the frequency of this electric signal is Surface acoustic waves are best generated when the center frequency of the input square dielectric 2 matches the frequency obtained by dividing the propagation velocity of the surface acoustic wave determined by the piezoelectric crystal used by the period of the comb-shaped electrode. The signal propagates on the output transformer 3 and excites the transformer 3, and an electric signal is again taken out from the power &5.

The substrate material used in such a surface acoustic wave device must satisfy the following conditions.

1.11 The mechanical coupling coefficient must be large. In other words, the efficiency of converting electrical signals into surface acoustic waves is high, and the propagation speed of surface acoustic waves is low. In other words, the device can be made smaller.

3.Surface acoustic wave delay time temperature coefficient is small.

In other words, the frequency does not change easily with temperature0 4. Low propagation loss of surface acoustic waves.

However, the only material that has low propagation loss and can be used from low to high frequencies is single crystal (single crystal), and an ideal material that fully satisfies all battle conditions has not yet been found. Table 1 shows the main crystal materials currently used for surface acoustic wave devices and their properties.

Table 1 shows LiNb0. As can be seen from Table 1, this material has a large mechanical coupling coefficient, but also a large delay time temperature coefficient. Conversely, T,1Ta03 crystal has a small delay time temperature coefficient, but also a small electromechanical coupling coefficient.

Now, as mentioned above, there is no material that has excellent overall properties, but LiNbo3. LiTa0. These materials are used as substrates for surface acoustic wave devices as materials with appropriate chirality.

This invention is based on the present invention (such a temperature sensor is, for example, NbO).

This method takes advantage of the large t3I' delay time coefficient of deterioration that inevitably occurs when a material with a large mechanical coupling coefficient, such as a crystal, is used, and uses this as a temperature measuring element.

In other words, although it varies depending on the cut surface of the crystal, the propagation speed of the surface acoustic wave, the distance between the input and output transformers, and the repeating period of the comb-shaped electrode change due to the flow rate, which changes the amplitude and phase characteristics of the output. Temperature sensors made of surface acoustic wave elements measure temperature by converting changes in such characteristics into changes in oscillation frequency (21.ζ).

3- FIG. 2 is a configuration diagram of a conventional temperature sensor made of a surface acoustic wave element. A temperature sensor 6 having a configuration similar to that shown in FIG. 1 is mounted on an insulating substrate 7, and has an input terminal 8 and The output terminal 9 is connected to the stem on the insulating substrate by wire bonding. Next (Insulating board 7 here
The sensor is constructed by inserting and sealing the entire area cap 11 provided with the upper infrared transmitting window 10.

In this case, the infrared rays emitted from the temperature measuring body are configured to enter through the transmission window 10 and reach the temperature sensor 6 mounted on the insulating substrate 7.The present invention has improved sensitivity and response speed k. The purpose of the present invention is to provide a temperature sensor that can provide a temperature sensor, and its main purpose is to use the back surface of an element substrate such as LiNbO3 as a light guide window.

Examples of the structure of the present invention will be described below with reference to the drawings.

Figures 3 (5) and (c) show the structure of the substrate according to the present invention, and Figure 3 (a) shows the structure of a thin plate 12 similar to the conventional one. Part 13, Figure 1, 4
- A temperature sensor 6 of similar construction is patterned.

Next, as a mounting method for the sensor, for applications where the object to be measured is in the direction of the lead wires as shown in Fig. 2, an insulating substrate 7 as shown in Fig. 4 is used.
A wire mesh camp (unlike in the conventional case, a window for transmitting infrared rays is not provided) is installed in the central part of the frame (a light guide window 14 is provided, and the sensor 6 is fixed in the same way as in the conventional case). n
Not yet.

In other words, infrared rays from the object to be measured enter from the back surface of the LiNb0° crystal substrate, but piezoelectric crystals such as LiNbO3 are transparent to infrared rays and have extremely low absorption loss.
Compared to conventional structures in which silicon or infrared transmitting glass is used as a transmission window, the structure is more direct, and sensitivity and response speed are faster.

In addition, Fig. 3 σ shows a structure in which the back surface of the substrate is curved into a lens shape to increase the light condensing power.When using the conventional structure shown in Fig. 2 (5), the sensor 6 is There are four rows 71 of mounting facing the bottom surface.Also, when mounting on the ceramic board 15 shown in Fig. 5, the printed wiring 1
It is attached by joining the terminal portion of 6 and the human output terminal of the eccentric sensor 6.

In this case, the substrate 13 having a lens-shaped back surface also serves as an exterior and exhibits a light condensing effect, making it efficient as a temperature sensor.

In addition, when implementing the present invention, a heat absorbing material such as carbon, which is thinly deposited on the sensor surface to a thickness of 1/10 or less of the surface acoustic wave, should be deposited in a negative atmosphere to delay the propagation (this will delay the flow of blood). It has a number of time-temperature threads, and this is used to make an armpit temperature sensor.In order to improve the sensitivity and response speed of this sensor, it is a piezoelectric sensor formed of a bullet + J-cloth surface wave element. By adopting a configuration in which the crystal substrate itself serves as a light guide window, the characteristics could be significantly improved.

[Brief explanation of drawings]

Figure 1 is a front view showing the configuration of a surface acoustic wave filter, Figure 2 is a front view showing the configuration of a surface acoustic wave filter.
The figure is a perspective view of a conventional sensor, (5) is a receptacle mounting part 0 is a metal cap part, FIG. 3 is a perspective view of a surface acoustic wave element according to the present invention, and FIGS. 4 and 5. , 6 is a temperature sensor, 7 is an insulating substrate, 1° is an infrared transmitting window, 11 is a metal camp, 12 is a thin plate, 13 is a substrate with a lens-shaped back surface, 14 is a light guiding window, and 15 is a ceramic substrate.

Claims (1)

[Claims] An input transducer and an output transducer are disposed on a substrate made of a piezoelectric crystal, and a surface acoustic wave element detects temperature by utilizing the temperature dependence of the temperature coefficient of delay time of a surface acoustic wave propagating between the transducers. A temperature sensor 0 characterized in that the back surface of the substrate is configured as an infrared introduction window.